The present invention relates to a process for the production of flameproofed, CFC-free rigid foams containing urethane and isocyanurate groups.
German Offenlegungsschriften 4,109,076, 4,026,702, 4,129,285, and 4,020,283 and published European patent application 421,269 describe processes for the production of halogen-free rigid polyurethane ("PUR") foams using water and hydrocarbons. The use of water as blowing agent has the disadvantage that the surface of the PUR foams is embrittled (surface brittleness) by the formation of polyurethane structures because of the reaction of isocyanate with water with elimination of carbon dioxide, adversely affecting the adhesion between the foam and the surface skin.
Although surface brittleness can be prevented by using hydrocarbons as sole blowing agent, the percentage content of flameproofing agents, which normally act as plasticizers, must be increased to ensure flame resistance, so that hydrocarbon-blown rigid PUR foams are generally not dimensionally stable and show shrinkage/contraction, particularly where cyclopentane is used as the blowing agent.
It has already been found that dimensionally stable hydrocarbonblown rigid PUP foams can be obtained by using branched-chain polyols without any adverse effect on flame retardancy (flame resistance).